Electrochemical Probing of Polymethylalumoxane by Pyridine

The dependence of the electrical conductivity of the polymethylalumoxane—pyridine system on the component ratio was studied. The structure and energy effects of the formation of complexes (including charged ones), which arise in interactions between pyridine, reactive fragments of polymethylalumoxane, and the natural concomitants of the latter (the most probable impurities that remain after the synthesis), namely, trimethylaluminum, H₂O, and “simple” alumoxane, [Me₂Al(μ-OAlMe₂)]₂, were calculated by the DFT method. It was found that, in the presence of traces of oxygen-containing donors (alumoxane and/or H₂O), the concentration of ions in solution increased by many orders of magnitude and attained the value observed experimentally. The interaction of pyridine with polymethylalumoxane fragments caused the almost complete replacement of trimethylaluminum, which formed >Al*(Me)(μ-Me)₂AlMe₂ bridges with three-coordinate Al atoms in polymethylalumoxane (Al*), by pyridine. It was shown that an analysis of the dependence of the conductivity of polymethylalumoxane solutions containing “free” trimethylaluminum on the content of pyridine added allowed the concentrations of trimethylaluminum, both free and bound with polymethylalumoxane, to be determined.